Abstract: The large-scale development of deep-sea wind power is crucial for achieving the carbon peaking and carbon neutrality goals. However, extreme weather conditions and maintenance challenges constrain the reliability of existing DC systems. A symmetrical bipolar system with a marine grounding electrode offers advantages such as lower costs and higher reliability. Nevertheless, its impact on the marine ecosystem, particularly on fish behavior, remains unclear. We used sturgeon as a research object, and designed an experimental platform to simulate a non-uniform DC current field. Moreover, based on the backgroud subtraction method, the target recognition and tracking are designed to analyze fish behavior. Then, the fish behavior characteristics are transformed to the velocity index and trajectory index, and to analyze the relationship between fish behavior and space current density. Finally, a threshold judgment method for fish avoiding in a non-uniform electrical field is put forward. The experimental results show that sturgeon shows an obvious accelerated straying behavior when approaching the electrodes, especially when the current density reaches a certain threshold value. Through quantitative analysis, the current density threshold of sturgeon avoidance response is 0.517 A/m².